This invention relates generally to aircraft landing gear braking systems, and more particularly concerns an improved system for controlling aircraft brake pressure.
A conventional skid detection system used in aircraft braking systems typically includes a wheel speed transducer for each wheel brake of the wheels of the aircraft, for measuring wheel speed and generating wheel speed signals that are a function of the rotational speed of the brake wheel. The wheel speed signal is typically converted to a signal representing the velocity of the aircraft, and compared with a desired reference velocity, to generate wheel velocity error signals indicative of the difference between the wheel velocity signals from each braked wheel and the reference velocity signal. The output of the velocity comparator is referred to as velocity error. The velocity error signals typically are adjusted by a pressure bias modulator (PBM) integrator, a proportional control unit, and a compensation network, the outputs of which are summed to provide an anti-skid control signal received by the command processor. The PBM integrator in the antiskid loop dictates the maximum allowable control pressure level during braking. When no skid is detected, this integrator allows full system pressure to the brakes.
The conventional PID controller for aircraft brake control systems deals with various conditions such as aerodynamics, landing gear dynamics, μ-slip profile, different landing conditions, and the like. One major problem is that tuning of controller parameters to guarantee high efficiency in different landing conditions and conditions affecting the tire-runway coefficient of friction (μ) of the aircraft braking system is often a difficult task.
Such algorithms usually take only one input, i.e., wheel velocity (Vw), and determine a reference velocity (Vref) with an apparatus. Then the Vref and Vw signals pass through the PID control logic, which generates a command signal. The command signal is supplied to a hydraulic servo valve and the output of servo valve, fluid pressure generates a brake torque through a brake. The algorithms show good antiskid performance—robustness and adaptability.
In spite of success of the PID type controller, related industry engineers and researchers have been continuously investigating other control schemes, partially because of difficulty in antiskid braking control parameter tuning. A need therefore still exists for an antiskid braking controller that can facilitate and shorten the process of antiskid braking control parameter tuning. The present invention meets these and other needs.